In the following paragraph, does the expression "they were home" means "they come back home"? Or what? Could you please explain the meaning of the bold part? It is fairly vague for me to understand.

"Olivia Brennan was the polar opposite of the woman I’d pictured for my son. But there she was… I had assumed that if he was bringing a girl home, things between them had to be fairly serious – but then it struck me that if it was only Olivia, maybe they weren’t actually home ‘together’ but rather just home ‘at the same time’."

Source: A Mother's Confession, by Kelly Rimmer